1. Field of the Invention
The Inmarsat Capacity Expander (“ICE”) invention is an improved means of digital microwave communications, particularly microwave communications using satellite transponder capacity leased on a “power/bandwidth” basis. For instance, the ICE invention is able to provide higher data rates using a given radio frequency (“RF”) bandwidth under transponder capacity leases on International Marine Satellite Organization (“Inmarsat”) satellites compared with the data rates of existing Inmarsat-B High Speed Data (“HSD”) capable satellite terminals. The ICE invention also includes an innovative management system that enables the use of ICE equipment with a non-real-time management and control channel and, optionally, with a real-time management and control channel.
Inmarsat provides dial-up services and a small amount of leased capacity on its “operational satellites” and provides only leased capacity on “lease satellites.” Operational satellites are in different orbital locations from lease satellites. Typically, for “dial-up” services on operational satellites, a land earth station operator (“LESO”) purchases minutes of usage from Inmarsat “as-used”, sells minutes of usage “as-used” to end-users on a call duration basis (by the minute), and pays Inmarsat after usage is incurred. A LESO typically offers “dial-up” or “on demand” satellite services on a demand-assigned basis between (i) fixed (land-based) facilities (each known as a land earth station, or “LES”) and (ii) marine, land-mobile, or airborne earth stations (each known as a mobile earth station, or “MES”) that comply with Inmarsat specifications. Customers of “dial-up” services use Inmarsat services for periodic calls, e.g., for individual calls or data sessions.
A LESO can also offer another service that allows customers to “lease” full-period, power/bandwidth “slots” with specific frequency boundaries on Inmarsat satellite transponders. For example, a LESO might purchase a long term lease of 400 kHz bandwidth and 26 dBW power from Inmarsat on a lease satellite, reserve 50 kHz bandwidth and 17 dBW power of the lease for shared occasional use or short term subleases (as opposed to paying Inmarsat for “as used” minutes on Inmarsat's dial-up service), and sublease the remaining power and bandwidth to LESO customers for long term subleases and private uses. Power/bandwidth leases and subleases are typically allocated to a customer on a full-time basis, with no contention for access to the leased slot from other Inmarsat or LESO customers. Power/bandwidth leases and subleases are collectively called “leases” herein. Remote terminals compliant with Inmarsat A, B, M4, and F specifications installed on vehicles, vessels, or aircraft and similarly compliant fixed remote terminals operating in leased mode can generally support a data rate of no more than 16 kbps in each 25 kHz slot of leased bandwidth. A slot leased on a power/bandwidth basis typically incurs charges computed based on the satellite RF transmission power and/or the transponder bandwidth used. There is unmet market demand for technologies that can obtain higher throughput while operating within a given power/bandwidth. Typically, for lease services, a LESO purchases satellite transponder capacity from Inmarsat in 25 kHz, 14 dBW increments on one or more Inmarsat satellites and resells that capacity to end-users.
An overriding concern of Inmarsat and other satellite system operators is that customers accessing a satellite shall not interfere with other customers. MES equipment must therefore meet strict performance criteria with regard to transmission center frequencies, bandwidth and power.
2. Description of Related Art
Art related to using, managing, and controlling Inmarsat services will first be described, followed by comments that generalize the application of such art to satellite and microwave communications systems.
An Inmarsat B (“Inmarsat-B”) MES terminal typically comprises an MES control unit (“MCU”), an RF terminal, and an RF cable between the MCU and RF terminal. Inmarsat MES terminals use a frequency band of 1626.5 to 1649.5 MHz for uplink and a frequency band of 1526.5 to 1546.5 MHz for downlink. The principal components of an MCU include a single carrier per channel (“SCPC”) satellite modem, an embedded microcontroller, telephone handset, voice codec, serial data input/output (“DTE I/O”) port, and standard management and control (“M&C”) software. An external power supply provides DC power to the MCU. The principal components of the RF terminal (“RFT”) are an antenna, an optional antenna controller, a Low Noise Amplifier (“LNA”) and a high power amplifier (“HPA”). User inputs to the MCU are through a telephone handset or a serial data port. Output from the satellite modem in the MCU is an L-band RF transmit carrier which is then multiplexed with M&C carriers and DC power. The “standard M&C channel” controls the HPA and antenna; the DC powers the HPA and the optional antenna controller. The satellite modem modulator output, fed through the cable, drives the HPA, and the HPA drives the antenna RF elements. Signals received at the antenna RF elements are fed from the antenna through the LNA and diplexed onto the RF cable (the same cable that carries the L-band RF transmit carrier, M&C and DC power to the RF terminal) to the demodulator section of the satellite modem. In a ship-borne MES (also known as a “maritime MES” or “marine MES”), the MCU is known as below decks equipment (“BDE”) and the RF terminal is known as above decks equipment (“ADE”). An airborne MES is also known as an “aero MES”, and a land-based MES is also known as a “fixed MES” or “land mobile MES” or “transportable MES”. The term “path” means a route over which communications is provided by electromagnetic means, provided, however, baseband paths may alternatively use optical means. A “traffic path” is a path over which user payload or traffic is carried. A “control path” is a path over which M&C messages are carried. The term “channel” means a method of exchanging messages between two devices using a common path and implies that the path may be shared with other types of messages or user traffic. The term “channel” used in connection with encrypted configuration codes and other message types exchanged with remote terminals, as described below, also includes delivery by means other than data communications networks, such as mail, fax, telex, telegram, oral, etc. The term “user” means an end user, such as a customer of a LESO, as opposed to personnel operating equipment at an LES. “On-line” means an earth station is actively transmitting a carrier over a traffic path. “Off-line” means an earth station is not actively transmitting a carrier over a traffic path. “Local” means a function or device associated with an end-user's site, e.g., a remote terminal. “Local” is contrasted with activities associated with a site not operated by a end-user, such as an LES.
The standard information technology associated with an Inmarsat-B LES includes computers and software that allocate uplink and downlink frequencies based on call requests, users' contract rights, bandwidth availability, etc., as provided for in Inmarsat specifications for Inmarsat-B operations. The Inmarsat-B management system includes a Network Coordination Station (“NCS”) for each ocean region and Access Control and Signaling Equipment (“ACSE”) at each LES and NCS. Each ACSE in an ocean region has network connectivity with the NCS for that ocean region, and exchanges standard M&C messages with the NCS to support Inmarsat-B MES users served by a given LES. To use an operational satellite, an MES requests a MES/LES traffic path on a call by call basis by sending a call request through the ACSE at the NCS serving the MES. The NCS ASCE allocates capacity from the “pool” of dial-up frequencies reserved by Inmarsat (“Inmarsat Pool”) and notifies the MES and the ACSE at the LES serving the MES of the frequency assignments for the requested call. When the call becomes active, the LES ACSE and the MES M&C functions communicate via a standard M&C in-band channel until the call hangs up. When the call hangs up, the LES ACSE notifies the NCS ACSE and releases the frequencies back to the Inmarsat Pool. In the call setup process, the MES notifies the NCS ASCE of the “service type” (e.g., voice, fax, 9.6 kbps data, HSD) being requested and the NCS ACSE and LES ACSE manage resources accordingly. The software built into the MCU configures the standard modem to match the service type. Similarly, the LES ACSE configures the modems (also known as “channel units”) at the LES to match the service type. For standard dial-up service (voice, fax, 9.6 kbps data, and HSD), a given NCS ACSE manages an Inmarsat Pool of RF carrier center frequencies for traffic paths on operational satellites serving a given ocean region, and the LESO is billed by Inmarsat based on the number of call minutes used.
To use a lease satellite, the LES ACSE acts as a “standalone NCS ACSE” and performs the functions of the NCS ACSE for carrier frequencies within the transponder spectrum leased and managed by that LES ACSE. Standard lease mode use of a lease satellite begins with a call request from an MES to the LES ACSE. The LES ACSE replies to the MES with frequency assignments for the requested lease mode. When the “lease mode call” becomes active, the LES ACSE and the MES M&C functions communicate via a standard M&C in-band channel until the call is dropped (torn down) or until the expiration of the sublease term or of the lease term (when the capacity allocation assigned by Inmarsat to the LES ACSE expires). For HSD lease services, a LESO's ACSE manages a pool of RF carrier center frequencies within the spectrum leased by the LESO, and Inmarsat invoices the LESO at a fixed monthly rate for the power and bandwidth resource that has been allocated to the LESO.
An Inmarsat-approved MES providing dial-up services contains a satellite modem that operates in different modes to meet requirements for remote terminal registration, for call signaling and supervision, and for transmission of user traffic for the various standard services. The modem operates as a random access time division multiple access (“RA/TDMA”) transmitter to send registration messages to the relevant NCS ACSE, and to send call requests to the NCS ACSE, as described above. Dial-up standard services use operational satellites and are voice (10 or 20 kHz bandwidth), 9.6 kbps data (20 kHz bandwidth) and HSD (64 kbps data, 100 kHz slot) (“Standard Services in dial-up mode”). The modem in a standard MES monitors a 6 kbps time division multiplexed (“TDM”) channel when not transmitting (“idle” or off-line) to listen to the NCS ASCE (dial-up service on operational satellites) or LES ASCE (NCS failure or lease services on lease satellites) for instructions. When on-line, the modem multiplexes (in the uplink) and demultiplexes (from the downlink) an in-band signaling channel in the SCPC carrier to support signaling and supervision messages to and from the LES ACSE. Counterparts of the equipment and functions described for an MES, adapted for the LES environment, are used at each LES to establish a traffic path between an LES and an MES. For instance, an LES sends an LES to MES dial-up call request to the NCS ACSE over an NCS RA/TDMA carrier (allocated for signalling of LES to MES call requests between the LES ACSE and the NCS ACSE). The NCS ACSE then uses the TDM carrier monitored by the MES, and the TDM carrier monitored by the LES ACSE to send a notification to the MES and to the LES ACSE of the allocated frequencies for the call. The LES is sometimes called a coastal earth station (“CES”). A CES or LES providing leased services is called a “lease gateway”.
The satellite modem in an Inmarsat-approved MES that provides leased services operates not only in dial-up modes, but also in additional modes necessary for leased services. HSD (64 kbps) service is the only standard Inmarsat lease mode (“Standard Services in lease mode”). To enter lease mode, an Inmarsat-B MES monitors a “bulletin board channel” on an operational satellite to learn the frequency of “Coastal Earth Station standAlone Lease” (“CESAL”) TDM carriers on each Inmarsat “lease satellite”. Based on the data received in the bulletin board channel and configuration information provided by the user that specifies the lease satellite and the lease gateway, the MCU in maritime and aero MESs repositions the antenna to point at the specified lease satellite (the user of most land mobile MESs must manually reposition the MES antenna), and tunes the MCU receiver to the CESAL carrier. If the MCU receives the appropriate message on the CESAL carrier, it will configure the modem and other electronics for leased mode operation. All standard Inmarsat-B services (dial-up and lease) use the same call set-up procedure. In standard lease mode, the MES uses call request procedures similar to those available on operational satellites, however, carrier assignment is provided by the specified lease gateway operating independently, rather than by an Inmarsat NCS. After receiving the selected CESAL carrier and entering lease mode, the user establishes a call via various methods available to a given MES, and upon receiving a carrier assignment via signalling carriers from the standalone ACSE, the MCU switches to data mode and turns on the MES HPA. To stay in leased mode, the MCU must constantly receive the correct CESAL carrier. If the MCU does not receive the correct CESAL carrier, or if user reconfigures the terminal to exit lease mode, the MCU turns off the HPA. More detail on the procedures and specifications for Inmarsat services and equipment, including Inmarsat-B MES and LES specifications, is available from Inmarsat, 99 City Road, London, England (www.inmarsat.org). Standard M&C signal paths are “in band”, that is, standard M&C messages share the path that is also used by payload traffic between an MES and an LES. It is possible to use non-standard peripheral equipment at a lease gateway and at an MES served by the lease gateway to provide a non-standard service if such peripheral equipment can be correctly configured and managed through an M&C channel external to standard control signal paths. Standard Services in dial-up mode and Standard Services in lease mode are collectively called, “Standard Services”.
Leased bandwidth on Inmarsat satellites is very expensive, and standard data rates are slow. Several types of standard Inmarsat MESs, in particular, Inmarsat-B MESs, use relatively inefficient fixed rate forward error correction (“FEC”) to encode and decode bitstreams for transmission in a widely diverse environment. An Inmarsat-B standard MES in lease mode provides a throughput of 64 kbps in 100 kHz of leased bandwidth. Higher data rates for a given bandwidth have been long sought. Although there is certainly demand for higher data rates, several substantial problems have hindered improvements, as follows:
Earth stations (both LES and MES) must have the ability to handle standard dial-up calling as well as leased services. Many ships only have a single MES, which must be available on short notice for emergency calls. If an LES channel unit or MES could provide higher data rates than are possible with Standard Services in lease mode, the LES channel unit or MES must be responsive to commands to revert from “enhanced leased operation” to Standard Services mode on short notice.
There are over 10,000 MESs currently installed on ships. For commercial success, a method of enhanced lease operation must be a retrofit of only the below decks equipment of an installed MES. A retrofit must not disturb those parts of an MES, such as the standard modem and the HPA, that have received Inmarsat certification as compliant with Inmarsat standards (“type approval”). Retrofitting presents significant problems in how to switch between two modems, yet ensure that the MCU receiver constantly receives CESAL carrier during enhanced lease operation.
Standard services drive the HPA with characteristic waveforms that are monitored by the MCU. Any combination of modulation methods, forward error correction, and data compression used to obtain higher data rates must result in a waveform that is compatible with the standard HPA included as part of a type approved Inmarsat terminal. For instance, many Inmarsat-B MCUs drive the HPA with a constant envelope waveform to provide Standard Services in lease mode. To avoid conditions that would cause such Inmarsat-B MCUs to turn off the HPA, enhanced lease operations must also drive the HPA with a constant envelope waveform.
To coordinate the use of standard and higher speed transmission paths among standard and retrofitted earth stations in a given network, a management system is required. For operational flexibility and efficiency, a method of enhanced lease operation should include a standalone management system that does not require a real-time, interactive connection between and MES and a network management computer. An MES in lease mode often stays in lease mode for the full period of the lease, which can be for years. A real-time, interactive management channel would needlessly consume precious bandwidth during long periods when no management is needed, and require a second real-time authorization and management network (in addition to the authorization and management network for Standard Services). If, however, an MES is used alternately for dynamic or reconfigurable lease services where capacity is allocated based on demand, a real-time, interactive M&C channel would be helpful.
Standard Inmarsat-B HSD supports only a 64 kbps path in a 100 kHz slot. Some Inmarsat-B users require full-period (constant) connectivity but employ data rates of less than 64 kbps. Such users must currently lease an entire 100 kHz slot to obtain full-period connectivity, even though they do not need a 64 kbps data rate. Some Inmarsat-B users have a need for asymmetric services in which two or more Inmarsat-B MESs share given leased bandwidth (one or more slots), and the transmit and receive data rates and bandwidths within the leased slot(s) are different for different Imnarsat-B MESs. However, asymmetric services are impossible using standard Inmarsat-B MESs. There are unmet demands for asymmetric services and for a full-period service that provides lower data rates, uses less bandwidth, and costs less than Inmarsat-B HSD service.
There have been unpublished efforts using peripheral equipment interfaced to an Inmarsat-B MES to solve the preceding problems and to achieve higher data rates. The results of these efforts to date, however, are systems that require a dedicated local personal computer (“PC”) as a site controller, real-time M&C channels between an MES and the LES, and transmission from the LES over the real-time M&C channels of all configuration commands and parameters (e.g., start time/stop time, ocean region configurations, and power level vs. data rate settings). These systems also problematic in that they may provide unlimited local user control of critical modem parameters.
A better solution to the preceding problems would be a system that does not require a real-time M&C channel, stores configuration commands and parameters locally, does not require a dedicated local PC, denies local user control of critical modem parameters, seamlessly supports dial-up, standard lease, and enhanced (higher data rate per given bandwidth) lease operations, and can be retrofitted on the huge installed base of MESs. The ICE invention not only solves these problems in the context of Inmarsat, but can be used to obtain higher data rates in other types of microwave transmission sold on a power/bandwidth basis. In a 100 kHz Inmarsat-B slot, an ICE-enabled MES can support approximately twice the datarate (128 kbps) compared with a standard MES (64 kbps). Moreover, ICE-enabled capacity is scalable. For instance, an ICE-enabled MES can support approximately 32 kbps in a 25 kHz Inmarsat-B slot and thereby provide greater efficiency of space segment utilization for applications that do not require high speed service. Alternatively, an ICE-enabled MES can support approximately 256 kbps in a 200 kHz Inmarsat allocation if an even higher data rate is required.